JPH0822185A - Developing device - Google Patents

Abstract

PURPOSE:To provide a developing device capable of attaining noncontact development efficient in developing without a developing bias. CONSTITUTION:The developing device carrying a two-component developer D to a developing region A by a developing sleeve 81 in which a magnet body 82 is fixedly provided and making toner soar up in a vibrating electric field, to develop a latent image is provided with a control electrode plate 84 constituted in such a manner that an electrode part 84a capable of applying a voltage is disposed on the tip part at the downstream side of the control electrode plate 84 fixedly provided at the upstream part of the developing region A. The position of the tip part on the downstream side of the control electrode plate 84 is set at a position where 50% <= T1max/T0max 4h80% is satisfied when a stuck toner quantity at the time of the control electrode plate 84 is not present at the time of developing with the same condition is defined as T0max and a stuck toner quantity at the time of inserting the floating control electrode plate 84 into the developing region defined as T1max.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image in a non-contact manner using a one-component or two-component developer in an image forming apparatus such as an electrophotographic copying machine.

[0002]

2. Description of the Related Art A "powder cloud development method" (US Pat. No. 2,725,
No. 304) was known, but recently, a method has been proposed in which an electrode plate is installed in the developing area and an oscillating electric field is formed between the developing sleeve and the electrode plate to electrically form a toner cloud for development. Has been done.

For example, in Japanese Patent Laid-Open No. 56-27158, a plurality of parallel wires are provided between an image forming body and a developing sleeve in a non-contact state, and the polarities of adjacent wires are reversed. A method of applying an alternating voltage so as to cause the developer to fly is disclosed.

Further, in Japanese Patent Laid-Open No. 57-198470, a grid is provided between an image forming body holding a latent image and a developing sleeve holding toner, and a direct current is provided between the grid and the developing sleeve. And a developing method characterized by applying an alternating current or one of them as a bias voltage.

Further, in Japanese Unexamined Patent Publication No. 3-121678, an electrode is installed in a developing area which is closest to an image forming body and a developing sleeve which is a developer carrying carrier, and an alternating electric field is applied to disperse and fly the toner. There is disclosed a method of performing the development.

[0006]

In the non-contact development described above, the development is performed by the flying toner adhering to the latent image on the moving image forming body. Therefore, as shown in FIG. 10, since the latent image moves while the toner T separated / flying from the developer D reaches the latent image, the amount of toner adhering to the leading end on the downstream side of the movement of the latent image is small, There is a problem that the toner adhesion amount becomes large at the trailing end portion, which is the upstream side of the movement of the latent image, and the development is biased (directionality).

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a developing device which performs non-contact development with good development efficiency without uneven development.

[0008]

The object is to convey a developer to a developing area by a developer conveying carrier, and to dispose a plate-shaped member in the developing direction between the image forming body and the developer conveying carrier in the developing area. In a developing device which is inserted from the upstream side and which performs non-contact development by forming an oscillating electric field between the image forming body and the developer transport carrier, the plate-shaped member is developed under the same conditions, When the toner adhesion amount when there is no member is T0max and the toner adhesion amount when the plate member is inserted in the developing area and the electrode portion of the plate member is floating is T1max, 50% ≦ T1max / T0max This is achieved by a developing device characterized in that the position is set to ≦ 80%.

In the developing device, it is a preferred embodiment that an oscillating electric field is formed between the electrode portion of the plate member and the developer carrying carrier.

[0010]

FIG. 2 is a schematic structural view showing an example of a color image forming apparatus equipped with the developing device of the present invention as a suitable developing means.

In FIG. 2, reference numeral 1 denotes a photoconductor belt which is a belt-shaped image forming body made of a flexible belt coated or vapor-deposited with a photoconductor, and the photoconductor belt 1 includes rotating rollers 2 and 3. It is installed between and is conveyed in the clockwise direction by driving the rotating roller 2.

Reference numeral 4 denotes a guide member fixed to the main body of the apparatus so as to be inscribed in the photoconductor belt 1. The photoconductor belt 1 is tensioned by the action of a tension roller 5, so that the inner peripheral surface of the guide member 1 becomes the guide member. Rub 4

6 is a scorotron charger as a charging means, and 7
Is a laser writing device using a laser beam as an image exposing means, and 8A to 8D are developing devices of the present invention which are a plurality of developing means each containing a developer of a specific color, and these image forming means are photosensitive members. It is arranged at a portion of the belt 1 in contact with the guide member 4.

Each of the developing devices 8A, 8B, 8C and 8D will be described in detail later. For example, each of the developing devices 8A, 8B, 8C and 8D accommodates yellow, magenta, cyan and black developers, respectively. Keep each developing sleeve
81, and has a function of visualizing the latent image on the photoreceptor belt 1 by a non-contact reversal development method. Unlike the contact development, the non-contact development has an advantage that it does not hinder the movement of the photosensitive belt 1.

A transfer device 12 and a cleaning device 13 are a blade 13a of the cleaning device 13 and a toner discharge roller.
13b is kept at a position apart from the surface of the photoconductor belt 1 during image formation and is pressed against the surface of the photoconductor belt 1 as shown in the figure only during cleaning after image transfer.

The process of forming a color image by such a color image forming apparatus is performed as follows.

First, the formation of a multicolor image according to this embodiment is shown in FIG.
Image forming system. That is, an original image is obtained by a color image data input section (a) scanned by an image sensor, and this data is arithmetically processed by an image data processing section (b) to create image data, which is temporarily stored in an image memory (c). To be done. Next, this image data is taken out at the time of recording and inputted to the recording unit (d), for example, the color image forming apparatus of FIG. That is, when image data, which is a color signal output from an image reading apparatus separate from the color image forming apparatus, is input to the laser writing apparatus 7, the laser writing apparatus 7 is a semiconductor as a writing light source (not shown). A laser beam (writing light) generated by a laser passes through a collimator lens and a cylindrical lens (not shown), is rotationally scanned by a rotary polygon mirror 74 which is rotated by a drive motor 71, passes through an fθ lens 75 and a cylindrical lens 76, and is in between. The optical path is bent by the individual mirrors 77 and 78, and is projected onto the peripheral surface of the photoconductor belt 1 to which uniform charge is previously applied by the charger 6 of the scorotron, and main scanning is performed to form a bright line.

On the other hand, when the scanning is started, the laser beam is detected by an index sensor (not shown), and the first
The laser beam modulated by the color signal of (1) scans the peripheral surface of the photosensitive belt 1. Therefore, a latent image corresponding to the first color is formed on the peripheral surface of the photosensitive belt 1 by the main scanning by the laser beam and the sub-scanning by the conveyance of the photosensitive belt 1. This latent image is developed by the developing device 8A in which yellow (Y) toner (visual medium) is loaded in the developing means, and a toner image is formed on the belt surface. The obtained toner image passes under the blade 13a of the cleaning device 13 and the toner discharge roller 13b as the cleaning means, which is separated from the peripheral surface of the photosensitive belt 1 while being held on the belt surface, and the next image forming cycle is performed. to go into.

That is, the photoconductor belt 1 is recharged by the charger 6, and then the second color signal is input to the laser writing device 7, and the belt is processed in the same manner as in the case of the first color signal described above. Writing is performed on the surface to form a latent image. The latent image is developed by the developing device 8B loaded with magenta (M) toner as the second color.

The magenta (M) toner image is formed in the presence of the previously formed yellow (Y) toner image.

Reference numeral 8C is a developing device having cyan (C) toner, which forms a cyan (C) toner image on the surface of the belt in the same manner as the first and second colors.

Further, 8D is a developing device having a black toner, which forms a black toner image on the surface of the belt by superposing it by the same processing as the above-mentioned color. A DC or even AC bias voltage is applied to each developing sleeve 81 of each of these developing devices 8A, 8B, 8C and 8D, and non-contact development is performed by a two-component developer that is a developing means.
The photosensitive belt 1 whose base is grounded is developed in a non-contact manner.

The color toner image thus formed on the peripheral surface of the photosensitive belt 1 is sent from the paper feeding cassette 14 through the paper feeding guide 15 by applying a high voltage having a polarity opposite to that of the toner at the transfer portion. It is transferred to the transfer material.

That is, the transfer material contained in the paper feed cassette 14 is carried out by the rotation of the paper feed roller 16 and one of the uppermost layers is carried out, and the timing is adjusted with the image formation on the photosensitive belt 1 via the timing roller 17. And is supplied to the transfer device 12.

The transfer material which has received the toner image is surely separated from the photosensitive belt 1 which suddenly changes its direction along the rotating roller 2 and goes upward, and the toner image is fused by the fixing roller 18. After being fixed, the paper is discharged onto the tray 20 via the paper discharge roller 19.

On the other hand, the photosensitive belt 1 which has been transferred to the transfer material is further conveyed and the blade 13a and the toner discharge roller 13b are brought into pressure contact with each other, and the residual toner is removed by the cleaning device 13 to finish the operation. Then, the blade 13a is separated again, and a little later, the toner discharge roller 13b is separated, and a new image forming process is started.

As the color image forming apparatus using the developing device of the present invention, a belt-shaped image forming body is described, but an image forming apparatus having a drum-shaped image forming body can be similarly used.

The developing devices 8A to 8D have the same structure, and will be denoted by reference numeral 8 below.

(Embodiment 1) FIG. 1 is a schematic sectional view showing an embodiment of the developing device of the present invention, showing an example in which one of the magnetic poles of the magnet body exists in the developing region.

In the figure, reference numeral 81 is a developing sleeve which is a developer carrying carrier made of a non-magnetic material such as aluminum, and is rotatable in the direction of the arrow in the figure. Reference numeral 82 denotes a magnet body fixed in the developing sleeve 81 and having a plurality of N and S magnetic poles in the circumferential direction. One magnetic pole 82a of the magnet body 82 is located at the closest position between the developing sleeve 81 and the photosensitive belt 1. It is arranged in the development area A and is referred to as a main magnetic pole. This developing sleeve 81
The magnet carrier 82 constitutes a developer carrying carrier. Magnet body
Each magnetic pole, including the main magnetic pole 82a of 82, is magnetized to a magnetic flux density of 500 to 1,500 gauss, and the magnetic force causes the developing sleeve.
A layer of magnetic developer D on 81, that is, this magnetic brush forming a magnetic brush moves in the same direction by the rotation of the developing sleeve 81 and is conveyed to the developing area A. This developing sleeve
The gap between the developing sleeve 81 and the regulating blade 86 and the gap between the developing sleeve 81 and the photosensitive belt 1 are adjusted so that the magnetic brush formed on the 81 does not contact the surface of the photosensitive belt 1 and maintains the gap.

Reference numeral 84 is a plate in which a voltage-applicable electrode portion 84a is disposed on the downstream end portion of an insulating member 83 provided on the upstream side of the developing area A in contact with / close to the layer of the developer D. The control electrode plate is a strip-shaped member, the insulating member 83 is a member also serving as a leveling member made of an electrical insulator such as polyester, polyimide, glass epoxy, polyethylene terephthalate, and polyamide imide, and the electrode portion 84a is made of a conductive material such as metal. It is made of a material and is integrally provided linearly on the tip of the insulating member 83. 85A and 85B are agitation screws for agitating the developer D to make the components uniform, and 86 is a developer regulating means made of a non-magnetic material or a magnetic material provided to regulate the height and amount of the magnetic brush. A blade, 87 is a cleaning blade for removing the magnetic brush passing through the developing area A from the developing sleeve 81, 88 is a developer reservoir, 89 is a casing, and 89 is a casing.
Reference numeral a denotes a support portion provided in the casing 89 for supporting the fixed portion of the insulating member 83. 90 is a holding plate which is an example of a fixing member, and 90s is a control electrode plate in which the holding plate 90 is fixed to the supporting portion 89a.
A set screw for fixing 84 so as to press it toward the developing sleeve 81.

As shown in FIG. 5, the electrode portion 84a is made of a conductive material such as a metal and has a circular or quadrilateral cross section, and is attached to the tip of the insulating insulating member 83 with an adhesive or the like. Affix with (Figs. 5 (a), (b), (g), (h)),
A cut 83a is provided at the tip of the insulating member 83 and is sandwiched between the cuts 83a (FIGS. 5C and 5D), and a recess is formed at the tip of the insulating member 83.
In addition to the method of providing 83c and embedding it here (FIGS. 5 (e) and 5 (f)), as shown in FIG. The electrode portion 84a can be formed at the tip of the insulating member 83 by laminating a conductive member such as copper foil using polyimide, paper phenol, or the like, and then performing an etching process. The electrode portion 84a is preferably covered with an insulating resin in order to prevent unnecessary discharge and to prevent rust. 84b is a terminal portion for applying a bias voltage.

The insulating member 83 of the control electrode plate 84 is a developing sleeve.
When the developer D is conveyed onto the 81, the developer D is slightly curved because the developer D enters between the insulating member 83 and the developing sleeve 81, and the insulating member 83 faces the developing sleeve 81 with a slight gap. Or, the developing sleeve 81 faces the developing sleeve 81 in a state where there is almost no gap, that is, in a state of being in contact with / close to the layer of the developer D. The point on the developing sleeve 81 which is in contact with / close to is called a contact point and is represented by 81b.

The thickness t (FIG. 6B) of the control electrode plate 84, which is the sum of the thickness of the insulating member 83 and the thickness of the electrode portion 84a, is the same as the thickness of the photosensitive belt 1 and the developing sleeve 81 in the developing area A. When the contact distance is d1, (1/100) d1 to (2/3) d1,
Particularly, (1/10) d1 to (1/2) d1 are preferable. (2/3) d
When it is larger than 1, the gap between the photoconductor belt 1 and the electrode portion 84a becomes narrow, so that the electrode portion 84a is likely to come into contact with the surface of the image forming body 1 and image disorder is likely to occur. Also, the electrode part
The oscillating electric field formed between 84a and the developing sleeve 81 is weakened, and the cloud generation capability is reduced. On the contrary (1/100) d
When it is 1 or less, an alternating current from the developing sleeve 81 is apt to flow in, a voltage drop occurs and the developability is deteriorated.
In addition, the strength of the plate-shaped member is low, and it is easy for the plate-shaped member to vibrate in an oscillating electric field.

Further, if the entire electrode portion 84a is enlarged so as to cover the downstream side and the upstream side of the contact point 84c as shown in FIG. The department will start generating unnecessary clouds.
In order to prevent this and obtain a stable transport amount, FIG.
As shown in (b), the entire electrode portion 84a has the contact point 81.
The closest contact point of the developing sleeve 81 to the photosensitive belt 1 rather than b
It is preferable to form it so as to be arranged only on the 81a side. The circumferential length of the electrode portion 84a depends on the diameter of the sleeve 81 and the conveying speed, but is preferably 0.05 to 5 mm, and particularly preferably 0.1 to 1 mm. 0.05m
If it is less than m, it is not possible to secure an oscillating electric field region that generates a sufficient cloud, and if it is more than 5 mm, it may exceed the closest contact 81a or the toner may be charged by vibration and become overcharged, resulting in deterioration of developability. Is likely to occur.

Further, the set position of the control electrode plate 84 is the toner when the development is performed under the same condition, the toner adhesion amount when the control electrode plate 84 is not present is T0max, and the floating control electrode plate 84 is inserted into the developing area. It has been found that when the adhesion amount is set to T1max, when the position is set to 50% ≦ T1max / T0max ≦ 80%, good development with sufficient image density without development bias can be performed.

FIG. 3 shows the control electrode plate from the upstream side of the developing area A.
When a bias voltage is not applied to the electrode portion 84a of the electrode 84, that is, when the electrode 84 is inserted in a floating state, the change in the toner adhesion amount with respect to the latent image when the electrostatic latent image formed under the condition of obtaining the maximum density during development is developed It is a graph shown. The horizontal axis indicates the downstream end of the control electrode plate 84 and the photosensitive belt 1.
The distance d3 (mm) between the closest contact point 81a between the developing sleeve 81 and the developing sleeve 81 and a straight line C connecting this to the rotation center O of the developing sleeve 81 (this is referred to as the closest tangent line C), and the vertical axis represents the latent image. The toner adhesion amount per unit area (mg / cm ² ) is taken (d3 is positive on the upstream side of the closest tangent line C and negative on the downstream side).

When T1max / T0max> 80%, the amount of toner adhering to the leading end of the latent image moving downstream side is small, and the amount of toner adhering to the trailing end of the latent image moving upstream side becomes large. Directionality) occurs.

On the other hand, when T1max / T0max <50%, the deterioration of the developing efficiency becomes remarkable. That is, good developability can be obtained without unevenness in the hatched area in FIG. As described above, inserting the control electrode plate 84, which is a plate-shaped member, into the developing area A prevents uneven development, but has a drawback that the developing efficiency is insufficient and the image density is low. In the present invention, the developing efficiency is improved by forming the following oscillating electric field between the electrode portion 84a of the control electrode plate 84 and the developing sleeve 81.

That is, the developing sleeve 81 is provided with a protective resistance R1 by a DC bias power source E1 and an AC bias power source E2.
A bias voltage in which an AC component is superimposed on a DC component is applied via the. In addition, a DC bias power source E is attached to the electrode portion 84a.
A bias voltage of only a DC component is applied from 3 through the protection resistor R2. It is preferable to apply a DC voltage having the same polarity as the toner to the electrode portion 84a from the viewpoint of preventing toner adhesion.

When the DC voltage applied to the developing sleeve 81 is equal to the DC voltage applied to the electrode portion 84a, the DC bias power source E1 can be shared as shown in FIG. It is possible to avoid complication.

In the developing device 8 of the present invention, by applying the bias voltage as described above, it is possible to control the alternating electric field (which will be referred to as a second oscillating electric field) formed between the photosensitive belt 1 and the developing sleeve 81. A first oscillating electric field is generated between the electrode portion 84a of the electrode plate 84 and the developing sleeve 81.

In the color image forming apparatus, if the OPC photosensitive member that is negatively charged is used as the photosensitive member of the photosensitive belt 1 and reverse development is performed, and the photosensitive member is charged to, for example, -800 V, the electrode portion 84a. Is applied to the developing sleeve 81, and a bias voltage of -750V + AC voltage component is applied to the developing sleeve 81. The AC component has a frequency of 100 to 20 KHz, preferably 1 to 10 KHz, and a peak-to-peak voltage (V _PP ) of 200 to 2,000.
V. In this case, since the electrode portion 84a is provided closer to the developing sleeve 81 than the photosensitive belt 1, the strength of the first oscillating electric field is higher than the strength of the second oscillating electric field.

The first vibrating electric field causes the toner particles of the developer D that have reached the vicinity of the electrode portion 84a to vibrate in the direction of the lines of electric force thereof, so that the toner particles are separated from the carrier and fly to form cloud haze-shaped toner. It can generate enough clouds. The toner cloud is assisted in the flight toward the latent image on the photoconductor belt 1 by the second oscillating electric field, and the control electrode plate 84 is set at an appropriate position, so that uniform development is performed.

At this time, since the AC bias is applied only to the developing sleeve 81, the first oscillating electric field and the second oscillating electric field have the same phase, and the toner particles are oscillated from the first oscillating electric field to the second oscillating field. Smooth transition to electric field.

The waveform of the above AC component is not limited to a sine wave,
It may be a rectangular wave or a triangular wave. Although the frequency is also related, the higher the voltage value is, the more the magnetic brush of the developer D is vibrated, and the separation and flight of the toner particles from the carrier particles are facilitated. Dielectric breakdown easily occurs. The generation of fog is prevented by a DC component, and the dielectric breakdown is caused by coating the surface of the phenomenon sleeve 81 with a resin, an oxide film, or the like so as to be insulating or semi-insulating, or the carrier particles of the developer D having an insulating property as described later. It can be prevented by using carrier particles.

FIG. 4 shows the amount of toner adhesion and the position of the downstream end of the control electrode plate 84 when developed under the same development conditions as in FIG. 3 when a bias voltage is applied to the electrode portion 84a of the control electrode plate 84. It is a graph which shows an example of a relation. As compared with the graph of FIG. 3, the toner adhesion amount increases, and even if the control electrode plate 84 is inserted to a position where there is no development bias, the control electrode plate 84 is not moved to the development area A.
It can be seen that the values are almost the same as when not inserted in.

However, in the region where T1max / T0max <50% or less when the electrode of the control electrode plate is in a floating state, it is not possible to obtain a sufficient toner adhesion amount and the image density is low.

FIG. 9 shows the results of changing the frequency and the peak-to-peak voltage of the AC component applied to the developing sleeve 81 in the above embodiment. In FIG. 9, a range shaded with a horizontal line is a range where fogging is likely to occur, a range shaded with a vertical line is a breakdown where dielectric breakdown is likely to occur, and a range shaded with diagonal lines is a range where image quality is likely to be deteriorated. There is a preferable range in which a stable and clear image can be obtained. As is clear from the figure, the range in which fogging is likely to occur changes according to changes in the AC component. Further, the low frequency region shaded with dots in the figure is a range where uneven development occurs due to the low frequency.

As described above, the developing device of the present invention keeps the magnetic developer D in non-contact with the photosensitive belt 1 which is an image forming body, and generates a toner cloud by the first and second oscillating electric fields. Therefore, the separation and flight to the photosensitive belt 1 are improved, the selective adsorption property to the electrostatic image is improved, and the carrier particles are prevented from adhering to the photosensitive belt 1. Although it is made possible to use a developer, a high-quality image can be developed, and it is preferable to use a developer D composed of the following carrier particles and toner particles.

Generally, when the average particle size of the magnetic carrier particles is large, the state of the ears of the magnetic brush formed on the developing sleeve 81 becomes rough. Therefore, even if the electrostatic latent image is developed while being vibrated by the electric field. However, there is a problem that unevenness is likely to appear in the toner image and the toner density at the ears becomes low, so that high-density development is not performed. To solve this problem, the average particle size of the magnetic carrier particles should be reduced, and as a result of experiments, it was found that the above problems do not occur when the weight average particle size is 50 μm or less. However, if the particle size of the magnetic carrier is too small, the magnetic carrier tends to adhere to the surface of the photoconductor belt 1 together with the toner particles and scatter easily. These phenomena are related to the strength of the magnetic field acting on the carrier and the strength of the magnetization of the carrier due to it, but in general, the above tendency gradually begins to appear when the weight average particle diameter of the magnetic carrier becomes 15 μm or less. It becomes noticeable at 5 μm or less. Therefore, in this developing device, the magnetic carrier of the developer D preferably has a weight average particle diameter of 50 μm or less, particularly preferably 30 μm or less and 5 μm or more. When the magnetic carrier is spherical, the stirring property of the toner particles and the carrier particles and the transport property of the developer D are improved, and the charge controllability of the toner is further improved. It is preferable because it prevents aggregation of particles.

Such a magnetic carrier is a metal such as iron, chromium, nickel, cobalt or the like, or a compound or alloy thereof, such as iron tetroxide or γ-oxidation, which is the same as in a conventional magnetic carrier as a magnetic substance. Spherical particles of ferromagnets or paramagnetic materials such as ferric iron, chromium dioxide, manganese oxide, ferrite, manganese-copper alloys, or the surfaces of these magnetic particles are styrene resin, vinyl resin, Ethylene resin, rosin modified resin,
Particles obtained by coating with acrylic resin, polyamide resin, epoxy resin, polyester resin, silicone resin or the like copolymer resin, or by making resin particles containing magnetic fine particles dispersed therein Are obtained by particle size selection by means of conventionally known average particle size selection means.

The use of spherical carrier particles coated with a resin or the like as described above, in addition to the effects described above, makes the layer of the developer D formed on the developer carrying carrier uniform, and Also, the effect that a high bias voltage can be applied to the developer carrier is given. That is, the fact that the carrier particles are spherical carrier particles coated with a resin or the like means that (1) in general, the carrier particles are easily magnetized and adsorbed in the long axis direction, but the spheroidization eliminates the directionality thereof, and therefore the developer layer Are uniformly formed to prevent locally low resistance regions and uneven layer thickness.
(2) As the resistance of the carrier particles is increased, the edge portion as seen in the conventional carrier particles is eliminated, and the electric field is not concentrated on the edge portion. As a result, a high bias voltage is applied to the developer carrier. However, the photoconductor belt 1
It is effective in preventing the electrostatic latent image from being disturbed by discharging on the surface and the bias voltage from breaking down. The fact that this high bias voltage can be applied means that the effects as described above in the development under the oscillating electric field of the present invention can be sufficiently exerted. And, the above-mentioned wax is also used for the spheroidizing of the carrier particles having the above effects, but from the viewpoint of the durability of the carrier, it is preferable to coat the above-mentioned spherical magnetic particles with a resin. Further, it is preferable that the carrier particles are formed of magnetic particles having an insulating property in which the resistivity of the carrier particles is 10 ⁸ Ωcm or more, particularly 10 ¹³ Ωcm or more. The resistivity, after tapping putting particles into a container having a cross section of 0.50 cm ^2, 1Kg / on packed particles cm ²
Is obtained by reading the current value when a voltage that generates an electric field of 1,000 V / cm is applied between the load and the bottom electrode. If this resistivity is low, the developer transport carrier When a bias voltage is applied to the carrier particles, charges are injected into the carrier particles, and the carrier particles are likely to adhere to the surface of the photosensitive belt 1 or the breakdown of the bias voltage is likely to occur.

In summary, the magnetic carrier particles are spherical so that at least the ratio of the major axis to the minor axis is 3 times or less, there is no protrusion such as needle-shaped portions or edge portions, and the resistivity is high. Is 10 ⁸ Ωcm or more, preferably 10 ¹³ Ωcm or more is a proper condition. Further, such magnetic carrier particles are obtained by increasing the resistance of spherical magnetic particles by forming an oxide film or the like. It is produced by subjecting to spheroidizing treatment or obtaining dispersed resin particles by a spray drying method.

Next, the toner particles will be described. Generally, when the average particle size of toner particles is small, the amount of charge qualitatively decreases in proportion to the square of the particle size, and the adhesive force such as the Van der Waals force is relatively large, and the toner particles are easily scattered. While fogging easily occurs, it becomes difficult to separate from the carrier particles of the magnetic brush. In the conventional magnetic brush developing method, such a problem becomes remarkable when the average particle diameter is 10 μm or less. In the developing device of the present invention, this problem is solved by developing with a magnetic brush under a double oscillating electric field. That is, the toner particles attached to the ears of the magnetic brush are
The toner is strongly vibrated in the first oscillating electric field and easily separates from the spikes to form a toner cloud.
The inertial force due to the rotation of the sleeve, the centrifugal force due to the oscillating electric field, and the like cause the toner particles to be carried to the immediately adjacent developing area A, and the toner particles are faithfully adsorbed to the electrostatic latent image under the second oscillating electric field. At this time, the electrode portion 84a is provided only on the downstream side of the insulating member 83 and the closest contact 81a of the developing sleeve 81, so that no cloud is generated in an unnecessary portion other than the developing area. Further, the toner particles having a low charge amount hardly move to the image portion or the non-image portion, and the toner does not rub against the photosensitive belt 1, so that the toner particles may adhere to the photosensitive belt 1 by frictional charging. It will be used up to a toner particle size of about 1 μm. The oscillating electric field weakens the bond between the toner particles and the carrier particles.
Adhesion of carrier particles accompanying the toner particles to the photoconductor belt 1 is also reduced, and the ears of the magnetic brush are kept in non-contact with the surface of the photoconductor belt 1 so that the toner particles have a large charge amount with respect to the carrier particles. As described above, the selective transfer to the electrostatic latent image under the oscillating electric field significantly reduces the adhesion of carrier particles to the photosensitive belt 1.

As the average particle diameter of the toner becomes large, as already mentioned, the roughness of the image becomes noticeable. Usually, for developing with fine lines arranged at a pitch of about 10 lines / mm, a toner with an average particle size of about 20 μm does not cause any problem, but if a finely divided toner with an average particle size of 10 μm or less is used, the resolution will be improved. Is significantly improved, and it gives a clear high-quality image that faithfully reproduces the tone difference. For the above reasons, the average particle size of the toner is 20 μm or less, preferably 10 μm or less. Further, since the toner particles follow the electric field, the charge amount of the toner particles is 3 μC /
Greater than g (preferably 3 μC / g to 30 μC / g)
Is desirable. Especially when the particle size is small, a high charge amount is required.

Such a toner can be obtained by a method such as a pulverization / granulation method, a suspension polymerization method, an emulsion polymerization method and the like similar to the conventional toner. That is, it is possible to use a toner in which spherical or amorphous non-magnetic or magnetic toner particles in the conventional toner are selected by the average particle size selection means. Further, the toner particles may be magnetic particles containing magnetic fine particles. In this case, the amount of the magnetic fine particles is 60 wt% or less, especially 30%.
Those that do not exceed wt% are preferable. When the toner particles contain magnetic particles, the toner particles are affected by the magnetic force contained in the developer carrying carrier, so that the uniform forming property of the magnetic brush is further improved and the fogging Generation is prevented, and toner particles are less likely to be scattered. However, if the amount of the magnetic substance contained is too large, the magnetic force between the carrier particles becomes too large,
It becomes impossible to obtain a sufficient developing density, and the magnetic fine particles come to appear on the surface of the toner particles.
It may be difficult to control triboelectric charging, or toner particles may be easily damaged.

In summary, in the developing device of the present invention, as the preferable toner particles, the resin as described for the carrier particles and the fine particles of the magnetic substance are used, and the coloring component such as carbon and the electrification as required. It is composed of particles having an average particle size of 20 μm or less, particularly preferably 10 μm or less, which can be produced by a method similar to a conventionally known method for producing toner particles by adding a control agent and the like.

The spherical carrier particles and toner particles as described above are used in the developing device of the present invention, but the same conditions are preferably used when a one-component non-magnetic developer or a one-component magnetic developer is used. Further, if necessary, a fluidizing agent for improving fluidity of particles and a cleaning agent useful for cleaning the surface of the image bearing member are mixed with the developer. As the fluidizing agent, colloidal silica, silicon varnish, metal soap or nonionic surface active agent can be used,
As the cleaning agent, a fatty acid metal salt, organic group-substituted silicon, or a surfactant such as fluorine can be used.

[0060]

According to the developing device of the present invention having the above-described structure, when developing under the same conditions, the toner adhesion amount when there is no control electrode plate is T0max, and when the floating control electrode plate is inserted in the developing area. The toner adhesion amount of
When it is set to 1max, it is set to a position where 50% ≦ T1max / T0max ≦ 80%, and an oscillating electric field is formed between the electrode portion of the control electrode plate and the developing sleeve, so that there is no development bias and the image density It has become possible to provide a developing device having a high and good developing property.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a developing device of the present invention.

FIG. 2 is a schematic configuration diagram showing an example of a color image forming apparatus including a developing device of the present invention.

FIG. 3 is a graph showing a relationship between an installation position of a control electrode plate and a toner adhesion amount.

FIG. 4 is a graph showing a toner adhesion amount when a bias voltage is applied to an electrode portion of a control electrode plate.

FIG. 5 is a cross-sectional view showing another form of the insulating member and the electrode portion of the control electrode plate.

FIG. 6 is a perspective view and an enlarged side view showing an example of a control electrode plate.

FIG. 7 is a diagram showing a length of an electrode portion and a generation state of a toner cloud.

FIG. 8 is a block diagram illustrating an image forming system.

FIG. 9 is a graph showing a preferred range of the AC component of the bias voltage of the developing sleeve.

FIG. 10 is a diagram illustrating conventional non-contact development.

[Explanation of symbols]

 1 photoconductor belt (image forming body) 6 scorotron charger 7 laser writing device 8, 8A, 8B, 8C, 8D developing device 81 developing sleeve 81a closest contact (to image forming body) 81b this contact (control electrode of developing sleeve) (To the plate) 82 Magnet 83 Insulation member 84 Control electrode plate (plate member) 84a Electrode part 86 Regulation blade A Development area D Developer E1, E3 DC bias power supply E2 AC bias power supply R1, R2 Protection resistance

Claims (2)

[Claims] 1. A developer carrying carrier carries a developer to a developing area, and a plate member is inserted between the image forming body and the developer carrying carrier in the developing area from an upstream side in the developing direction, and In a developing device that performs non-contact development by forming an oscillating electric field between an image forming body and a developer transport carrier, the plate-shaped member is developed under the same conditions, and the toner adhesion amount when the plate-shaped member is not present. Is set to T0max, and when the toner adhesion amount is T1max when the plate member is inserted into the developing area and the electrode portion of the plate member is floating, the position is set to 50% ≦ T1max / T0max ≦ 80%. A developing device. 2. The developing device according to claim 1, wherein an oscillating electric field is formed between the electrode portion of the plate member and the developer transport carrier.